/* -*- mode: c++; c-basic-offset: 4; indent-tabs-mode: nil; -*- */
//
// compress.cpp
//
// Data Compress Routines based on LZSS
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define N           4096      // size of ring buffer
#define F           18        // upper limit for match_length
#define THRESHOLD   2         // encode string into position and length if match_length is
// greater than this index for root of binary search trees
#define NIL         N

unsigned long int
textsize = 0,           // text size counter
codesize = 0,           // code size counter
printcount = 0;         // counter for reporting progress every 1K bytes

unsigned char
text_buf[N + F - 1];    // ring buffer of size N, with extra F-1 bytes to facilitate string
// comparison of longest match. Set by the InsertNode() procedure.

int   match_position, match_length,
      lson[N + 1], rson[N + 257], dad[N + 1]; // left & right children & parents -- These
// constitute binary search trees.

void InitTree(void) // initialize trees
{
    int i;

    // For i = 0 to N - 1, rson[i] and lson[i] will be the right and
    // left children of node i.  These nodes need not be initialized.
    // Also, dad[i] is the parent of node i.  These are initialized to
    // NIL  (= N), which stands for 'not used.'
    // For i = 0 to 255, rson[N + i + 1] is the root of the tree
    // for strings that begin with character i.  These are initialized
    // to NIL.  Note there are 256 trees.

    for (i = N + 1; i <= N + 256; i++)
        rson[i] = NIL;
    for (i = 0; i < N; i++)
        dad[i] = NIL;
}

void InsertNode(int r)
{
    // Inserts string of length F, text_buf[r..r+F-1], into one of the
    // trees (text_buf[r]'th tree) and returns the longest-match position
    // and length via the global variables match_position and match_length.
    // If match_length = F, then removes the old node in favor of the new
    // one, because the old one will be deleted sooner.
    // Note r plays double role, as tree node and position in buffer.

    int i, p, cmp;
    unsigned char *key;

    cmp = 1;
    key = &text_buf[r];
    p = N + 1 + key[0];
    rson[r] = lson[r] = NIL;
    match_length = 0;

    for (;;) {
        if (cmp >= 0) {
            if (rson[p] != NIL)
                p = rson[p];
            else {
                rson[p] = r;
                dad[r] = p;
                return;
            }
        } else {
            if (lson[p] != NIL)
                p = lson[p];
            else {
                lson[p] = r;
                dad[r] = p;
                return;
            }
        }

        for (i = 1; i < F; i++)
            if ((cmp = key[i] - text_buf[p + i]) != 0)
                break;

        if (i > match_length) {
            match_position = p;
            if ((match_length = i) >= F)
                break;
        }
    }

    dad[r] = dad[p];
    lson[r] = lson[p];
    rson[r] = rson[p];
    dad[lson[p]] = r;
    dad[rson[p]] = r;

    if (rson[dad[p]] == p)
        rson[dad[p]] = r;
    else
        lson[dad[p]] = r;

    dad[p] = NIL; // remove p
}

void DeleteNode(int p) // deletes node p from tree
{
    int q;

    if (dad[p] == NIL)
        return; // not in tree

    if (rson[p] == NIL)
        q = lson[p];

    else if (lson[p] == NIL)
        q = rson[p];

    else {
        q = lson[p];

        if (rson[q] != NIL) {
            do
                q = rson[q];
            while (rson[q] != NIL);

            rson[dad[q]] = lson[q];
            dad[lson[q]] = dad[q];
            lson[q] = lson[p];
            dad[lson[p]] = q;
        }

        rson[q] = rson[p];
        dad[rson[p]] = q;
    }

    dad[q] = dad[p];

    if (rson[dad[p]] == p)
        rson[dad[p]] = q;
    else
        lson[dad[p]] = q;

    dad[p] = NIL;
}

int Encode(const char *filename, unsigned char *header, int headersize, unsigned char *buffer, int bufsize)
{
    int i, c, len, r, s, last_match_length, code_buf_ptr;
    unsigned char code_buf[17], mask;
    int bufptr = 0;
    FILE *pOut;

    pOut  = fopen(filename, "wb");
    if (pOut == NULL)
        return -1; // bail

    // Write Header first
    if (headersize > 0)
        fwrite(header, headersize, 1, pOut);

    InitTree(); // initialize trees

    // code_buf[1..16] saves eight units of code, and code_buf[0] works as eight flags,
    // "1" representing that the unit is an unencoded letter (1 byte), "0" a
    // position-and-length pair (2 bytes). Thus, eight units require at most 16 bytes of code.
    code_buf[0] = 0;
    code_buf_ptr = mask = 1;
    s = 0;
    r = N - F;

    for (i = s; i < r; i++)
        text_buf[i] = ' '; // Clear the buffer with any character that will appear often.

    for (len = 0; len < F && bufptr < bufsize; len++) {
        c = buffer[bufptr++];
        text_buf[r + len] = c; // Read F bytes into the last F bytes of the buffer
    }

    if ((textsize = len) == 0)
        return -1; // text of size zero

    // Insert the F strings, each of which begins with one or more 'space' characters.
    // Note the order in which these strings are inserted. This way, degenerate trees
    // will be less likely to occur.
    for (i = 1; i <= F; i++)
        InsertNode(r - i);

    // Finally, insert the whole string just read. The global variables
    // match_length and match_position are set.
    InsertNode(r);

    do {
        if (match_length > len)
            match_length = len; // match_length may be spuriously long near the end of text.

        if (match_length <= THRESHOLD) {
            match_length = 1; // Not long enough match.  Send one byte.
            code_buf[0] |= mask; // 'send one byte' flag
            code_buf[code_buf_ptr++] = text_buf[r]; // Send uncoded.
        } else {
            // Send position and length pair. Note match_length > THRESHOLD.
            code_buf[code_buf_ptr++] = (unsigned char)match_position;
            code_buf[code_buf_ptr++] = (unsigned char)(((match_position >> 4) & 0xf0) | (match_length - (THRESHOLD + 1)));
        }

        if ((mask <<= 1) == 0) {
            // Shift mask left one bit.
            for (i = 0; i < code_buf_ptr; i++)
                putc(code_buf[i], pOut); // Send at most 8 units of code together

            codesize += code_buf_ptr;
            code_buf[0] = 0;
            code_buf_ptr = mask = 1;
        }

        last_match_length = match_length;

        for (i = 0; (i < last_match_length) && (bufptr < bufsize); i++) {
            c = buffer[bufptr++];
            DeleteNode(s);    // Delete old strings and
            text_buf[s] = c;  // read new bytes

            // If the position is near the end of buffer, extend the buffer to make
            // string comparison easier.
            if (s < F - 1)
                text_buf[s + N] = c;

            // Since this is a ring buffer, increment the position modulo N.
            s = (s + 1) & (N - 1);
            r = (r + 1) & (N - 1);
            InsertNode(r); // Register the string in text_buf[r..r+F-1]
        }

        while (i++ < last_match_length) {
            // After the end of text, no need to read, but buffer may not be empty.
            DeleteNode(s);

            s = (s + 1) & (N - 1);
            r = (r + 1) & (N - 1);

            if (--len)
                InsertNode(r);
        }
    } while (len > 0);  // until length of string to be processed is zero

    if (code_buf_ptr > 1) {
        // Send remaining code.
        for (i = 0; i < code_buf_ptr; i++)
            putc(code_buf[i], pOut);
        codesize += code_buf_ptr;
    }

    fclose(pOut);

    return codesize;
}

int Decode(const char *filename, int headersize, unsigned char *buffer, int bufsize)
{
    // Be careful with your buffersize, will return an exit of -1 if failure

    int i, j, k, r, c;
    unsigned int flags;
    int bufptr = 0;
    FILE *pIn;

    pIn = fopen(filename, "rb");
    if (pIn == NULL)
        return -1; // bail

    // Skip Header
    if (headersize > 0)
        fseek(pIn, headersize, SEEK_SET);

    r = N - F;
    for (i = 0; i < r; i++)
        text_buf[i] = ' ';

    flags = 0;

    for (;;) {
        if (((flags >>= 1) & 256) == 0) {
            if ((c = getc(pIn)) == EOF)
                break;
            flags = c | 0xff00; // uses higher byte cleverly
        }

        // to count eight
        if (flags & 1) {
            if ((c = getc(pIn)) == EOF)
                break;
            buffer[bufptr++] = c;

            if (bufptr > bufsize)
                return (-1); // check for overflow

            text_buf[r++] = c;
            r &= (N - 1);
        } else {
            if ((i = getc(pIn)) == EOF)
                break;
            if ((j = getc(pIn)) == EOF)
                break;

            i |= ((j & 0xf0) << 4);
            j = (j & 0x0f) + THRESHOLD;

            for (k = 0; k <= j; k++) {
                c = text_buf[(i + k) & (N - 1)];
                buffer[bufptr++] = c;

                if (bufptr > bufsize)
                    return -1; // check for overflow

                text_buf[r++] = c;
                r &= (N - 1);
            }
        }
    }

    fclose(pIn);

    return bufptr; // return uncompressed size
}
